Rotary mixing devices, such as known from U.S. Pat. No. 5,167,448, are used for intensively mixing material components, specifically dental substances consisting of two or more components. In the known device, a capsule containing the substance is placed in a holder which is mounted on a rotary disk at an eccentric position with respect to the disk axis and so that the holder is rotatable about it own axis. The known mixing device is capable of performing both a mixing step proper, in which the capsule is moved back and forth due to its own rotation on the rotary disk, and a centrifuging step, in which the capsule itself does not rotate relative to the rotary disk and the substance is compressed in the direction of a dispensing piston provided within the capsule.
Conventional capsule holders for dental mixing devices are fork-shaped and consist of two leaf springs or of a rigid member and a resilient member, between which the capsule is clamped. U.S. Pat. No. 4,890,931 discloses a capsule holder of this type, which comprises a carrier portion adapted to the coupled to a rotary part of the mixing device, and a pair of retaining members movable relatively to each other along a capsule clamping direction and disposed on said carrier portion for engaging a capsule from two opposite sides along said clamping direction.
The known mixing forks require a comparatively large amount of space, specifically in the direction perpendicular to the capsule axis (which is usually the axis along which the mixing movement takes place). Further, they are unsuited for the rotary mixing devices described above because they fail to retain the capsule with sufficient safety during the mixing and centrifuging steps, in which forces exerted on the capsule are not only in the clamping direction.